12 FLORIDA GEOLOGICAL SURVEY—FOURTH ANNUAL REPORT. 
already mentioned, the lake region topography is found extending 
from Lake Kingsley in Clay County south through eastern Alachua, 
Putnam, the western part of Volusia, the western part of Orange, 
and the central part of Lake Counties, and thence south through 
eastern Polk County into DeSoto County. 
The records showing the depth at which the Vicksburg Limestone 
underlies the lake region, are fewer than could be desired. a At St. 
Augustine and at Orange Mills east of the lake region of Clay and 
Putnam Counties, the Vicksburg has been recognized at the depths 
of 225 and 130 feet respectively. At Sanford near the east border of 
the lake region in Orange County the Vicksburg lies at a depth of 
from 113 to 125 feet. At Orlando, which lies within the lake region 
of Orange County, this formation was identified from well samples 
at a depth of from 130 to 250 feet, the well having terminated 
in this formation at 250 feet.* As to the depth of the Vicksburg 
underlying the southward extent of the lake region into Polk and 
DeSoto Counties we have no record beyond a statement by Dali that 
at Bartow in Polk County, “it (the Ocala Limestone) is covered by 
about 6 feet of later strata.”! No one seems to have verified this 
determination of the formation at Bartow. However, from the 
topography the writer is led to believe that the Vicksburg may be 
expected underlying the lake regions of Polk County at a depth not 
exceeding 100 or 200 feet. 
UPPER OLIGOCENE. 
The Upper Oligocene is represented by the Apalachicola group of 
formations. This group includes the Chattahoochee, Tampa, Haw¬ 
thorne, and Alum Bluff formations. The first three of these may be 
partly contemporaneous in time. The formations of the Upper Oli¬ 
gocene are variable in character and include limestones, shell marls, 
clays, fullers earth, and sands. They exert a much less character¬ 
istic effect upon the topography than does the Vicksburg formation. 
In some of the formations, moreover the fossils are few and poorly 
preserved. Thus the identification of the formation from well sam¬ 
ples become difficult or impossible, and the thickness and extent of 
the different formations is not easily determined. 
CHATTAHOOCHEE FORMATION. 
The type exposure of the Chattahoochee formation is found in 
the vicinity of Chattahoochee in Gadsden County. The formation 
♦Letter from George C. Matson of Nov. 24, 1908. Based upon the identi¬ 
fication of fossils from the Orlando City well by Dr. Ray Basler. 
fBulletin No. 84, U. S. Geol. Survey, p. 104, 1892. 
